1. Field of the Invention
This invention pertains generally to the field of aluminum elcetrolytic capacitors and specifically to the construction of such a capacitor designed to increase the rate of heat flow from the core of the capacitor, thereby increasing the wattage handling capability of the device.
2. Description of the Prior Art
The internal heat generated during fluctuating voltage operation of an aluminum electrolytic capacitor can cause the core of a capacitor to become a relatively hot spot in operation. This necessitates a design for the construction of an aluminum electrolytic capacitor operated at relatively high currents which will conduct heat from the core of the capacitor to the outside environment.
The traditional thermal model of an aluminum electrolytic capacitor is characterized by radial heat flow, the design serving to conduct heat from the core to the side of the can in which the capacitor is encased. For the thermal radial model of such a capacitor, the optimum shape would be a relatively tall unit of small diameter.
The problem to which the present invention addresses itself is well known in the prior art. One of the most successful, commercially available electrolytic capacitors designed for improved heat dissipation is the type 101R capacitor of Sangamo which is provided in an advertised thermal pack construction. The Sangamo type 101R is constructed from a standard aluminum electrolytic capacitor foil roll in which the anode foil and the cathode foil, interleaved with a spacer, are wound on an arbor in a conventional fashion. The cathode foil is extended at the base end of the roll significantly below the anode foil. The aluminum can in which the foil roll is placed is further configured to improve heat dissipation. The base of the can is reinforced with a plurality of ribs having an upwardly projecting conical structure at its center to engage the base of the core of the foil roll. The extended cathode contacts these ribs at less than 20% of the total surface area. The nonconductive cover of the can has a correspondingly situated plurality of ribs and downwardly projecting conical structure to engage the opposite end of the core of the foil roll. The foil roll is in a relatively stable position in the can and the use of a potting compound is eliminated. This further improves the reliable operation of the safety vent as well, since it permits a relatively unobstructed flow of gasses when certain conditions of temperature and stress are encountered, lowering the rate of internal pressure rise. The Sangamo type 101R relies primarily upon the conventional or traditional thermal model and is a device characterized by radial heat flow assisted by an axial flow. Its optimum shape is a tall unit of small diameter.
While the Sangamo type 101R device is an effective prior art answer to the question of heat dissipation, the device of the present invention yields improved performance while at the same time reducing the cost of construction.